1. Field of the Invention
This invention relates generally to indwelling catheters and like articles--e. g., other tubes, and generally other therapeutic articles that remain in a living body for protracted periods.
The invention relates more particularly to systems for keeping the exterior surfaces (as well as any proximal orifices) of such therapeutic articles free of undesirable microorganisms and contaminating debris. Such catheters, tubes and other articles of therapy are used in medical procedures for both humans and animals.
(An "indwelling" catheter or other article is one that is emplaced and left in place for protracted periods, such as fifteen minutes or longer. It has been known to leave catheters in place for more than five years. In this document the word "proximal" is used to define locations with respect to the center of the patient's body, not with respect to the instrumentation at the other end of the catheter. The word "medical" is used to encompass surgical as well as medicinal therapies. The word "bacteria" here encompasses bacteria, viruses, fungi, and other bioactive materials.)
The invention is applicable, for example, to such catheters as the Foley urinary-tract catheter or other urinary catheters, as well as tracheal, cardiac, or central or other venous catheters.
The invention is also suitable for use with tubes that irrigate or drain body cavities such as (without exclusion) the pleural, peritoneal, subarachnoid, intrathecal, subdural and intracraneal cavities--or that are used for special procedures such as evacuation of hematoma. Furthermore, as already suggested, our invention is not limited to use with articles having conductive lumens; rather, it can be employed as well with solid rods--either flexible or stiff--that find therapeutic use in medicine.
For illustrative purposes, we shall first discuss at some length the need for our invention in one familiar area. That is the field of catheters which are placed in the urinary tract.
2. Prior Art
A full discussion of prior art with which we are acquainted appears in the patent mentioned above, and in the public record of references adduced and discussed in prosecution of that patent in the U.S. Patent and Trademark Office.
The invention which is the subject of that patent is addressed primarily to the problems that arise from accumulation of clogging deposits and contaminating bacteria on an indwelling catheter or like article at proximal orifices, and within the interior of such an article. Such deposits and bacteria interfere mechanically and directly with the therapeutic function of a catheter or other tube, and may interfere with the therapeutic functions of various other indwelling articles.
The present document is directed primarily to related problems of formation, multiplication and migration of microorganisms and contaminants on an indwelling article along its outside surface. The interference of such organisms and debris with the function of an indwelling article is neither as mechanical nor as direct, but is equally as severe.
Infections arising from propagation of microorganisms and contaminating debris along the outside surfaces of such articles cause immeasurable grief and enormous costs. These adverse effects are particularly tragic in that they are nosocomial--that is to say, caused during and apparently as a result of hospitalization.
The incidence and cost of nosocomial urinary-tract infections in general hospitals, arising from the use of indwelling catheters, has been reported recently by Rutledge and McDonald in "Cost of Treating Nosocomial Urinary Tract Infections," Urology 26 (1 supplemental):24-6, 1985. An earlier discussion was provided by Platt et al., in "Mortality Associated with Nosocomial Urinary Tract Infections," New England Journal of Medicine 307:637-642, 1982.
These surveys put the extra hospital time, in a typical instance of nosocomial urinary-tract infection, at five to six days per hospital stay--for an annual nationwide extra cost of 1.8 billion dollars. Nosocomial urinary-tract infections are estimated to arise in 3.6 percent of all hospital admissions. Evans, Journal of the American Medical Association 256 (#8 August 22/29), 1986.
The major cause of nosocomial urinary-tract infections in hospitals is believed to be the indwelling catheter. The mortality rate directly attributed to nosocomial bacteremic urinary-tract infection has been reported as 12.8 percent. Furthermore, extensive analysis of hospital histories implicates virtually the entire gamut of procedures for catheter storage, emplacement and maintenance. Refer to Cecil's Textbook of Medicine, 17th edition, II:1487 (Saunders), 1985.
In nursing homes, such notorious hazards of urinary-tract infection have apparently deterred the use of urinary catheters on a broad scale, even though such catheters are well known as a means of alleviating the distress of urinary incontinence. Even with such limited use, seven million nosocomial urinary-tract infections--many due to catheter use--occur per year in patients confined to nursing homes (see Cecil's Textbook of Medicine).
As a result, elderly patients in nursing homes are generally denied the benefits of such catheters. It is therefore reasonable to consider nursing-home costs arising out of the complications of urinary incontinence. Such costs are estimated in the range $0.5 billion to $1.5 billion per year.
These values represent three to eight percent of all nursing-care costs (see Ouslander, J. G. and Kane, R. L. in "The cost of urinary tract incontinence in nursing homes," Med Care 22:69-79, 1984). Yet, as already suggested, it is generally held that nursing homes would incur greater cost if they put urinary catheters into general use, employing existing catheter-insertion technique.
Problems with indwelling catheters have also been reported in outpatient situations. Indwelling urinary-tract catheters, varying from paraplegic appliances to obstructive-uropathy bypasses, figure prominently in such situations.
Maintenance of urinary catheters is often necessary for paraplegics, as loss of urinary control commonly accompanies their condition. Heretofore such paraplegics have been maintained on virtually constant antibiotic supply, to avoid urinary infection arising from catheterization; even so, their catheters must be changed on a regular basis.
This technique, however, is unhealthy and undesirable as it carries a danger of both tolerance to existing bacteria and bacterial mutation "around" the available antibiotics. Protracted use of each catheter, with little or no antibiotics, could be enjoyed if there were some way to insert and maintain such catheters free of contamination and infection.
Infection costs in this context include medication, increased morbidity, and mortality of other diseases. In this regard please see Platt et al., supra; Edward, "The Epidemiology of 2056 Remote Site Infections " Annals of Surgery 6:184, 1976.
In hospitals, nursing homes, and outpatient applications, as shown in the literature, contamination and infection continue to develop after emplacement of an indwelling catheter--even when emplacement has been carried out unreproachably. There are two main mechanisms for such continuing contamination and infection.
First, contaminating debris migrates up and around a catheter from outside the body. Such debris includes fecal fragments, diseased tissue in trace quantities, and so on. Bacteria and other microorganisms are included in, and follow, these substances.
Such contaminants originate from naturally unsanitary regions on the outside of the patient's body but near the distal opening (such as the urethral meatus) of a catheterized duct or incision (e. g., drain site). For purposes of this document, including the appended claims, the term "duct" is to be understood as encompassing any natural passageway into or through the body, regardless of its usual nomenclature. One large contributor to such contamination from outside the body is contamination from the patient's own hands or from the hands of health-care personnel.
Secondly, it is also well recognized that mucous membranes react to an indwelling catheter by secreting mucus. The protein in this mucus forms a nurturing substrate for propagation of bacteria in the space around the catheter, multiplying greatly the overall bacterial population--and, in short, producing an infection in the patient.
Some of the contaminating mechanisms mentioned in the previously mentioned "parent" U.S. Patent may also contribute to bacterial seeding of the mucous substrate in the space around the outside of an indwelling catheter. These mechanisms consequently aggravate the contaminated conditions in that space.
Furthermore, all of these undesirable conditions may propagate inward into the body via the catheter: they can literally spill over from the proximal end of a catheterized duct or incision into the adjacent cavity (or tissue). By way of example, such a cavity or tissue may be the urinary bladder, or a surgical site.
Contamination of naturally occurring substances within a cavity (e. g., urine in the bladder) and contamination of the cavity wall then ensues. Such an unhealthful sequence may continue with decreasing natural flow or circulation of such substances, in turn promoting further infection as previously noted.
The foregoing summary shows that prior medical art has failed to deal adequately with the problem of infectious media propagating in the spaces or tissue around an indwelling catheter or other therapeutic article. It would be extremely desirable, in terms of quantitative costs as well as human pain and loss, to correct this failing.
This discussion of hospital, nursing-home and outpatient situations makes clear that the need is great for some way to insert and maintain urinary-tract catheters, free from the many sources of contamination discussed above. If indwelling urinary-tract catheters could be inserted and maintained free of contamination and infection for long periods after insertion--the favorable results would include great reductions in infection and human suffering, and save at least hundreds of millions of dollars in time and costs every year.
These data suggest a further conclusion. No problem having such widespread and various causes can be eliminated by any single change in mere medical protocol.
The need is not limited to urinary catheters. A like need exists whenever sterile catheters, tubes, or other elongate articles of therapy are inserted under sterile conditions into a living body. Examples include (among others) pacemakers and central lines (catheters or tubes placed into large veins), as well as Swan-Ganz catheters.
Often these must be inserted under emergency conditions in emergency rooms and intensive- and cardiac-care units. In these situations sterility is too easily compromised.